In order to determine the Time-Of-Flight for the particle identification,​ the S800 includes a plastic scintillator at the [[Stations#​Object_station|object station]] (S800_OBJ) and at the [[Stations#​focal_plane_station|focal-plane station]] (E1). The detector material typically used is

In order to determine the Time-Of-Flight for the particle identification,​ the S800 includes a plastic scintillator at the [[Stations#​Object_station|object station]] (S800_OBJ) and at the [[Stations#​focal_plane_station|focal-plane station]] (E1). The detector material typically used is

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[[http://​www.detectors.saint-gobain.com/​uploadedFiles/​SGdetectors/​Documents/​Product_Data_Sheets/​BC400-404-408-412-416-Data-Sheet.pdf|BC-400]] or [[http://​www.detectors.saint-gobain.com/​uploadedFiles/​SGdetectors/​Documents/​Product_Data_Sheets/​BC400-404-408-412-416-Data-Sheet.pdf|BC-404]] made from polyvinyltoluene (>97% ) and organic fluors ​ (<3%) with a density 1.032 g/​cm<​sup>​3</​sup>​ and a refractive index 1.58. The thickness of the detectors is chosen on the basis of the charge of the nuclei to be measured. The available thicknesses are __127 μm and 1 mm__ for OBJ_SCI and __1 mm and 5 mm__ for E1. The OBJ_SCI has an active area of __xxx__ and is connected to a photomultiplier __xxx__. The E1 scintillator is connected to photomultipliers [[EMI 98807B]] in both ends (up and down). The time signal from the E1 scintillator is calculated as the average time signal from each photomultipliers.

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[[http://​www.detectors.saint-gobain.com/​uploadedFiles/​SGdetectors/​Documents/​Product_Data_Sheets/​BC400-404-408-412-416-Data-Sheet.pdf|BC-400]] or [[http://​www.detectors.saint-gobain.com/​uploadedFiles/​SGdetectors/​Documents/​Product_Data_Sheets/​BC400-404-408-412-416-Data-Sheet.pdf|BC-404]] made from polyvinyltoluene (>97% ) and organic fluors ​ (<3%) with a density 1.032 g/​cm<​sup>​3</​sup>​ and a refractive index 1.58. The thickness of the detectors is chosen on the basis of the charge of the nuclei to be measured. The available thicknesses are __127 μm and 1 mm__ for OBJ_SCI and __1 mm and 5 mm__ for E1. (Guidelines explaining the installation of E1 scintillator can be found [[Installation FP SCI|here]]). The OBJ_SCI has an active area of __xxx__ and is connected to a photomultiplier __xxx__. The E1 scintillator is connected to photomultipliers [[EMI 98807B]] in both ends (up and down). The time signal from the E1 scintillator is calculated as the average time signal from each photomultipliers.

Different Time-of-flights can be constructed by combining the timing signals from these two detectors with the timing signals from the [[https://​groups.nscl.msu.edu/​a1900/​|A1900]] focal plane, and the RF cyclotron. The E1 detector is also used to define a valid trigger from the S800. The timing resolution for a point-like beam spot in the focal plane is around 100 ps. However, this resolution worsens significantly (up to 1 ns) when the whole focal plane is illuminated,​ because of path length differences of the traversing nuclei. It can be recovered by tracking the position of each event on the scintillator from the position and angle information provided by the [[Detectors#​Cathode Readout Drift Chambers (CRDC)|CRDC]] detectors. The plastic scintillators can withstand maximum rates up to 1 x 10<​sup>​6</​sup>​ particles per second.

Different Time-of-flights can be constructed by combining the timing signals from these two detectors with the timing signals from the [[https://​groups.nscl.msu.edu/​a1900/​|A1900]] focal plane, and the RF cyclotron. The E1 detector is also used to define a valid trigger from the S800. The timing resolution for a point-like beam spot in the focal plane is around 100 ps. However, this resolution worsens significantly (up to 1 ns) when the whole focal plane is illuminated,​ because of path length differences of the traversing nuclei. It can be recovered by tracking the position of each event on the scintillator from the position and angle information provided by the [[Detectors#​Cathode Readout Drift Chambers (CRDC)|CRDC]] detectors. The plastic scintillators can withstand maximum rates up to 1 x 10<​sup>​6</​sup>​ particles per second.

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Each TPPAC has an active area of 10 cm x 10 cm and is filled with isobutane at a typical __pressure of 5 torr__. The detector consists of a cathode foil with a series of aluminum strips oriented in the non-dispersive direction, followed by an anode plate and a second cathode foil with the strips oriented in the dispersive direction. A total of 128 pads are connected to the strips of each cathode foil. The x and y positions are determined from the charge distribution on the pads. The position calibration was done using the pad pitch of 1.27 mm.

Each TPPAC has an active area of 10 cm x 10 cm and is filled with isobutane at a typical __pressure of 5 torr__. The detector consists of a cathode foil with a series of aluminum strips oriented in the non-dispersive direction, followed by an anode plate and a second cathode foil with the strips oriented in the dispersive direction. A total of 128 pads are connected to the strips of each cathode foil. The x and y positions are determined from the charge distribution on the pads. The position calibration was done using the pad pitch of 1.27 mm.

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The particles transmitted through the TPPAC ionize the gas, producing electrons and positive ions. The drift of electrons towards the central anode plane induces an image charge on the aluminum strips. The signal generated on a given pad is sent to a preamplifier,​ and processed by a switch capacitor array (SCA), which acts as an analogic memory. Since the signals of this detector are generated before a valid trigger occurs, they need to be temporarily recorded until the trigger is received. The SCA samples the signals from the detector with a period of 200 ns and saves the data on a continuous mode, generating an analogic buffer. When a valid trigger is received, the sampling stops and the SCA pointer moves back in the buffer by a number of samplings pre-defined according to the time passed between the tracking signal and the valid trigger. In this way, the valid trigger is correlated with the tracking signal corresponding to the same event. The reading algorithm is lead by the FPGA chips of a [[{{:​wiki:​Manual_JTEC_XLM72VUM.pdf|XLM72}}]] VME module. The TPPACs can work at maximum rates in the range from

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The particles transmitted through the TPPAC ionize the gas, producing electrons and positive ions. The drift of electrons towards the central anode plane induces an image charge on the aluminum strips. The signal generated on a given pad is sent to a preamplifier,​ and processed by a switch capacitor array (SCA), which acts as an analogic memory. Since the signals of this detector are generated before a valid trigger occurs, they need to be temporarily recorded until the trigger is received. The SCA samples the signals from the detector with a period of 200 ns and saves the data on a continuous mode, generating an analogic buffer. When a valid trigger is received, the sampling stops and the SCA pointer moves back in the buffer by a number of samplings pre-defined according to the time passed between the tracking signal and the valid trigger. In this way, the valid trigger is correlated with the tracking signal corresponding to the same event. The reading algorithm is lead by the FPGA chips of a {{:​wiki:​Manual_JTEC_XLM72VUM.pdf|XLM72}} VME module. The TPPACs can work at maximum rates in the range from

{{:​wiki:​crdc-section-drift.jpg?​400 |Principle of operation of a CRDC.}}

{{:​wiki:​crdc-section-drift.jpg?​400 |Principle of operation of a CRDC.}}

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Both CRDCs are equipped with digital electronics,​ which consist of seven front-end electronic boards (FEE) designed and developed by the [[http://​www.star.bnl.gov/​|STAR collaboration]] ([[http://​www.bnl.gov/​rhic/​|RHIC]]),​ followed by interface boards connected to a programmable FPGA VME module ({{:​wiki:​Manual_JTEC_XLM72VUM.pdf|XLM72}}) like the one used with the [[Detectors#​Tracking Parallel Plate Avalanche Counters (TPPAC)|TPPACs]] in the intermediate image station. Each FEE includes 32 channels of preamplifier shaper, followed by a switch capacitor array (SCA) and an ADC. The processing of signals is driven by the FPGA module. Each SCA samples the signals after a valid trigger is received and sends the information into the ADC. The digitized ​ data are then stored into the internal memory of the FPGA and read out in block mode. The sampling frequency and number of samples read out are adjustable; typical values are 20 MHz and 8 to 12 samples. The time needed for each sampling is around 16 µs. Thus, the dead time of the electronics is directly proportional to the number of samples read out. The main advantage of the on-detector digitalization technique used with the CRDCs is the reduction of noise by avoiding the transmission of analog signals (448 from the two CRDCs) outside the vacuum chamber, and the possibility to record multi-hit events like in traditional TPC detectors. The schematic diagram of the firmware for the reading of the XLM72V FPGA can be found {{:​wiki:​Crdc5v.pdf|here}}

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Both CRDCs are equipped with digital electronics,​ which consist of seven front-end electronic boards (FEE) designed and developed by the [[http://​www.star.bnl.gov/​|STAR collaboration]] ([[http://​www.bnl.gov/​rhic/​|RHIC]]),​ followed by interface boards connected to a programmable FPGA VME module ({{:​wiki:​Manual_JTEC_XLM72VUM.pdf|XLM72}}) like the one used with the [[Detectors#​Tracking Parallel Plate Avalanche Counters (TPPAC)|TPPACs]] in the intermediate image station. Each FEE includes 32 channels of preamplifier shaper, followed by a switch capacitor array (SCA) and an ADC. The processing of signals is driven by the FPGA module. Each SCA samples the signals after a valid trigger is received and sends the information into the ADC. The digitized ​ data are then stored into the internal memory of the FPGA and read out in block mode. The sampling frequency and number of samples read out are adjustable; typical values are 20 MHz and 8 to 12 samples. The time needed for each sampling is around 16 µs. Thus, the dead time of the electronics is directly proportional to the number of samples read out. The main advantage of the on-detector digitalization technique used with the CRDCs is the reduction of noise by avoiding the transmission of analog signals (448 from the two CRDCs) outside the vacuum chamber, and the possibility to record multi-hit events like in traditional TPC detectors. The schematic diagram of the firmware for the reading of the XLM72V FPGA can be found {{:​wiki:​Crdc5v.pdf|here}}.

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here

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===== Ionization chamber =====

===== Ionization chamber =====

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An ionization chamber downstream of both [[Detectors#​Cathode Readout Drift Chambers (CRDC)|CRDCs]] is used to identify the Z number of the transmitted nuclei from their energy loss. The detector has an active ​volume ​of __xxx cm x xxx cm x xxx cm__ and [[Gas handling system||is filled]] with P10 gas (90% argon, 10% methane) at a typical pressure of 300 torr, although this value can be increased up to 600 torr for light nuclei. The detector consists of 16 stacked-parallel plate ion chambers with narrow anode-cathode gaps, placed along the detector’s central axis, perpendicular to the beam direction (see figure). The plates are constructed from 70 mg/​cm<​sup>​2</​sup>​ polypropylene with 0.05 µm of aluminum evaporated on each side. The entrance and exit windows of the chamber are made of 14 mg/​cm<​sup>​2</​sup>​ Mylar with an overlay of Kevlar filaments and epoxy.

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An ionization chamber downstream of both [[Detectors#​Cathode Readout Drift Chambers (CRDC)|CRDCs]] is used to identify the Z number of the transmitted nuclei from their energy loss. The detector has an active ​area of __xxx cm x xxx cm__ and a depth of approximately 406 mm (16 inches). It [[Gas handling system||is filled]] with P10 gas (90% argon, 10% methane) at a typical pressure of 300 torr, although this value can be increased up to 600 torr for light nuclei. The detector consists of 16 stacked-parallel plate ion chambers with narrow anode-cathode gaps, placed along the detector’s central axis, perpendicular to the beam direction (see figure). The plates are constructed from 70 mg/​cm<​sup>​2</​sup>​ polypropylene with 0.05 µm of aluminum evaporated on each side. The entrance and exit windows of the chamber are made of 14 mg/​cm<​sup>​2</​sup>​ Mylar with an overlay of Kevlar filaments and epoxy.

{{:​wiki:​ion-chamber-picture.jpg?​500 |Picture of the S800 ionization chamber with its alternating cathode and anode plates.}}

{{:​wiki:​ion-chamber-picture.jpg?​500 |Picture of the S800 ionization chamber with its alternating cathode and anode plates.}}

The electrons and positive ions liberated by the ionization of the gas along the particle trajectory drift towards the closest ​ anode-cathode pair. The drifting electrons and ions absorb the energy stored in the detector capacity and produce a voltage change of the anodes across the resistor. The main advantages of the anode-cathode configuration is that the electrons and ions are collected on a very short distance (about 1.5 cm), thus reducing pile-up and position dependence of the signals. Moreover, dividing the detector into 16 sections reduces the detector capacitance and consequently its noise. The operating voltage depends on the charge of the measured nuclei (e.g. __xxx for xxx and xxx for xxx__). Each anode is attached to a small preamplifier inside the ion chamber. This significantly reduces the electronic noise, although it involves the venting of the whole chamber whenever a malfunctioning preamplifier needs to be replaced. The electronic signals from the preamplifier are sent into a [[https://​groups.nscl.msu.edu/​nscl_library/​manuals/​caen/​MOD.N568B.pdf|CAEN N568B]] 16-channel shaper/​amplifier with remotely adjustable gains. The output signals feed a [[https://​groups.nscl.msu.edu/​nscl_library/​manuals/​phillips/​7164H.pdf|Phillips 7164H]] ADC.

The electrons and positive ions liberated by the ionization of the gas along the particle trajectory drift towards the closest ​ anode-cathode pair. The drifting electrons and ions absorb the energy stored in the detector capacity and produce a voltage change of the anodes across the resistor. The main advantages of the anode-cathode configuration is that the electrons and ions are collected on a very short distance (about 1.5 cm), thus reducing pile-up and position dependence of the signals. Moreover, dividing the detector into 16 sections reduces the detector capacitance and consequently its noise. The operating voltage depends on the charge of the measured nuclei (e.g. __xxx for xxx and xxx for xxx__). Each anode is attached to a small preamplifier inside the ion chamber. This significantly reduces the electronic noise, although it involves the venting of the whole chamber whenever a malfunctioning preamplifier needs to be replaced. The electronic signals from the preamplifier are sent into a [[https://​groups.nscl.msu.edu/​nscl_library/​manuals/​caen/​MOD.N568B.pdf|CAEN N568B]] 16-channel shaper/​amplifier with remotely adjustable gains. The output signals feed a [[https://​groups.nscl.msu.edu/​nscl_library/​manuals/​phillips/​7164H.pdf|Phillips 7164H]] ADC.